1. Field of the Invention
The present invention relates to a full bridge inverter with a push/pull control chip, and more specifically relates to a push/pull control chip controlling the full bridge switch assembly for driving the load.
2. Description of the Related Art
The primary power supply of the cold cathode fluorescent lamp (CCFL) of the TFT LCD is used with the inverter circuit. The prior art inverter circuit converts DC power into AC power, and is discriminated into half bridge inverter, full bridge inverter and push/pull inverter, for example, by the topology of the different circuits.
Referring to FIG. 1, the transformer T1 divides the whole circuit into a front circuit 101 and a back circuit 102, and there is a push/pull control chip 103 connected between the front circuit 101 and the back circuit 102. The front circuit 101 comprises a DC power, a first switch Q1, a second switch Q2 etc. and the back circuit 102 comprises at least a capacitor (C1, C2, C3), a load, at least a diode (D1, D2) etc.
Referring to FIG. 2, the push/pull control chip 103 transmits a first control signal a and a second control signal b to the first switch Q1 and the second switch Q2, respectively, for switching the two switches. Power is thus supplied to the load through the transformer T1 according to the DC power. The voltage wave c of the secondary of the transformer T1 is the wave of the ac voltage at point C in FIG. 2.
In the above description, the push/pull control chip 103 is chip LX1686 and the series LX1686, LX1688, LX1691 of the LINFINITY (MICROSEMI) Corp., the series of the chip O2-9RR of the O2 Micro International Limited Corp., and the series of the chip BIT3105, BIT3494 of the Beyond Innovation Technology Corp.
As shown in FIG. 3, the transformer T2 divides the whole circuit into a front circuit 201 and a back circuit 202. The front circuit 201 comprises four electronic switches (P1, P2, N1, N2), a full bridge control chip 203 and a capacitor C1. Moreover the back circuit 202 comprises a load. Referring to FIG. 4, the full bridge control chip 203 transmits four control signals (POUT1, POUT2, NOUT1, NOUT2) to the four electronic switches (P1, P2, N1, N2), respectively; by switching those switches, power is supplied to the load through the transformer T2 according to the DC power. The full bridge control chip 203 is the BIT3105 of the Beyond Innovation Technology Corp.
In the above description, driving the full bridge switch assembly requires the full bridge control chip 203 and driving the push/pull inverter requires the push/pull control chip 103, thus lacking practical flexibility. Furthermore, the control chip of the inverter circuit is limited in use so as to be hard to purchase together.